Coudert L H
Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS, Université Paris-Sud, Université Paris-Saclay, F-91405 Orsay, France.
J Chem Phys. 2017 Jan 14;146(2):024303. doi: 10.1063/1.4973773.
Terahertz pulses effects are investigated in an asymmetric top C molecule using numerical simulations. The average value of the direction cosine Φ is computed solving the time dependent Schrödinger equation for several types of pulses. The HS molecule taken as a test case is first subject to two short terahertz pulses with a duration smaller than 5 ps, an identical maximum value of the electric field of 2 MV/cm, but a different shape. The thermal average ⟨⟨Φ⟩⟩ is calculated for several temperatures, and non-periodic time variations are found even for the lowest temperature. For a given temperature, the maximum orientation achieved is shown to be dependent on the overlap between the absorption spectrum of the molecule and the Fourier transform of the pulse. The maximum orientation is also shown to be closely related to the molecular energy increase. In a second step, the optimal control theory is used to build a 14 ps long few-cycle pulse with the same maximum value of the electric field allowing us to reach a large maximum value of ⟨Φ⟩ equal to 0.93. A fairly good understanding of the wavefunction describing the molecule after the pulse was achieved.
利用数值模拟研究了太赫兹脉冲对非对称陀螺C分子的影响。通过求解几种类型脉冲的含时薛定谔方程，计算出方向余弦Φ的平均值。以HS分子作为测试案例，首先对其施加两个持续时间小于5皮秒的短太赫兹脉冲，这两个脉冲的电场最大值相同，均为2兆伏/厘米，但形状不同。针对几个温度计算了热平均值⟨⟨Φ⟩⟩，结果发现即使在最低温度下也存在非周期性的时间变化。对于给定温度，所达到的最大取向显示出取决于分子吸收光谱与脉冲傅里叶变换之间的重叠。最大取向还显示出与分子能量增加密切相关。在第二步中，利用最优控制理论构建了一个14皮秒长的少周期脉冲，其电场最大值相同，使得我们能够达到⟨Φ⟩的一个大的最大值，等于0.93。对脉冲后描述分子的波函数有了相当好的理解。
